230 MINERALOGY AND LITHOLOGY. 
fine in texture, but the development of larger feldspar crystals makes it 
porphyritic. In thin sections, the hornblende is entirely of a fibrous char- 
acter; the feldspar is very impure, both as a result of decomposition and 
original inclusion of impurities. The quartz is tucked away in little cor- 
ners. In this rock the titanic iron assumes the most fantastic forms, but 
it is mostly altered into the gray product which is characteristic of all 
these diorites. This subject, however, needs no further illustration. 
Epidote, chlorite, and sphene are present in small amount. Pyrite is 
abundant. Apatite, which is so prominent in the basic eruptive rocks, 
is here but rarely seen. 
At Lancaster these rocks are abundant. Some are very dark in color 
when hornblende predominates ;, some are yellowish-green when feldspar, 
filled with epidote, predominates, and all those variations in composition 
are met with which might be expected as a result of the metamorphism 
of sedimentary beds. 
AMPHIBOLITE. 
Amphibolite is a granular massive or schistose rock, which 1s com- 
posed of amphibole with more or less quartz. Accessories, as usual, 
are present. We have the following varieties to describe: 
Amphibolite (massive hornblende rock). 
Hornblende Schist. 
Actinolite Schist. 
These rocks are very prominent among the greenstones. Their horn- 
blende possesses the same crystalline character as that of the diorites 
last described. Their relation to the diorites is shown by the frequent 
presence of triclinic feldspar. Indeed, some of the rocks rich in plagio- 
clase might be called quartz diorite if one chose to draw the line ata 
different point. This is not an unusual circumstance, for such grada- 
tions have been elsewhere observed. For example: among the so-called 
ophites of the Pyrenees there are amphibolites, which, by the gradual 
introduction of plagioclase, are stated to pass by insensible stages into 
typical diorites;—and so we have a familiar association of rocks here. 
Amphibolite. This rock is a very nearly massive aggregate of horn- 
blende crystals, or of hornblende and quartz. It occurs in the same 
